Nearly 1,100 new apartment units could be coming to Pentagon City as part of a major planned development of the 37-acre RiverHouse apartment complex.

RiverHouse owner Vornado presented the initial development plans to largely skeptical members of the Arlington Ridge Civic Association last night.

The plans call for 934 new market rate apartment units, to be added to the existing 1,670 units on the site across three buildings, which date back to the 1950s and 60s. Vornado is also proposing a 150 unit, stand-alone affordable apartment building, to be developed with a nonprofit affordable housing partner.

The new market rate units will be built across three buildings, each about seven stories tall — half the height of the existing buildings — to preserve the views of condominium residents on Arlington Ridge.

The first two buildings are to be built on what is currently a surface parking lot across from the Pentagon Row courtyard. Between the buildings will run a pedestrian corridor that leads up to the ridge, with 30,000 square feet of ground floor retail space.

The surface parking will be replaced with a large underground garage. RiverHouse aims to reduce its overall parking ratio from just over one spot per unit to 0.85 spots per unit, as currently only about 70 percent of its parking spots are filled at night. With a total of 2,754 units, RiverHouse would have 2,340 parking space.

The third building will be built on what is now a pool and detached fitness center behind two of the buildings. In place of the current amenities, the new building would have a larger, improved fitness center plus a large, new outdoor pool, for use by residents of all three buildings.

Grace Hopper Park, located on the RiverHouse grounds, would remain untouched. Beside it, in front of the southernmost RiverHouse building on S. Joyce Street and across from county softball fields, Vornado is proposing the 150-unit building, affordable for those making up to 60 percent of area median income.

A Vornado representative said the company is seeking to partner with a nonprofit affordable housing developer on the building. Should the community express widespread opposition, however — a representative said it would be “a shame” not to utilize the extra land on the RiverHouse campus for affordable housing — the company may agree to instead agree to make its affordable housing contribution in the form of a check to Arlington’s Affordable Housing Investment Fund.

Vornado is planning on moving some of the mature trees impacted by the project in order to give the new buildings an “instant tree canopy.” An exact count of the trees set for removal was not immediately available, but the company rep said they would all be replaced with new trees, per county policy.

(The office development was approved but has yet to be built. Another Vornado development in Pentagon City, a 700-unit residential building that will house a Whole Foods, is currently under construction.)

Many of the concerns were related to density, zoning changes and school overcrowding.

Vornado said the current county General Land Use Plan for RiverHouse allows 72 units per acre, while residents pointed out that its current zoning does not allow that density. Vornado is seeking County Board approval for a zoning change, residents were told.

Oakridge Elementary, on Arlington Ridge, is projected to be one of the most overcrowded in the county in the next few years and is the school that would serve children in the new buildings.

Vornado’s representative said that there are only 30 Oakridge students currently in RiverHouse, making it unlikely that the new market rate apartments would contribute significantly to additional overcrowding. However, the rep said the company is aware of the school issue and is seeking to work with Arlington Public Schools on it.

Already, the rep said, Vornado had given APS officials tours of vacant office space in Crystal City, which could potentially be converted to school use. However, Vornado has not made any formal proposals and the company is seeking to be part of a broader APS-led school capacity conversation and community process for the area.

“We want to be at the table as the largest [private] property owner in Arlington County,” the rep said. “We want to be part of that discussion.”

Vornado formally filed for a General Land Use Plan study of RiverHouse last week, thus kicking off the regulatory process for the development.

Should it be approved as a site plan amendment by the County Board — a community-driven process that could take 18 months or more — Vornado expects construction of the project to be done in phases. The first buildings, replacing the parking lot, could be built with 4-5 years, with another 2.5 years for the rest of the project.